Didn't they require you to take a class or something before your surgery to discuss your eating restrictions?
Actually since Lap Band and Gastric Bypass are two different surgeries, I'll answer the question.
Gastric Bypass people have very strict eating restrictions in the beginning, and most of them can never eat very sweet things ever again or it will result in gastric "dumping" syndrome which causes terrible cramping in the abdomen.
They usually have to be on a liquid diet for a while, then a soft diet, then move up to solids eventually. It takes a while. They are encouraged to stay away from refined sugars and high fat foods.